Effects of hydrogen dilution on performance and in-plane uniformity of large-scale PEM fuel cell with low anode catalyst loading

Abstract

Enhancing hydrogen utilization is crucial for improving the efficiency of Proton Exchange Membrane (PEM) fuel cells. However, the widespread implementation of ultra-thin PEMs introduces a challenging objective: balancing hydrogen utilization with hydrogen dilution, which can adversely affect performance. To achieve this balance, understanding the impact of hydrogen dilution on fuel cell performance is critical, particularly for commercial large-scale fuel cells with low anode catalyst loadings, where significant research gaps remain. This study aims to fill these research gaps by investigating the performance and current distribution of a 291 cm² fuel cell with an anode platinum loading of 0.1 mg/cm² under varying hydrogen molar fractions (HMFs) and hydrogen stoichiometric ratios (HSRs). The results reveal that hydrogen dilution affects performance through three primary mechanisms: decreasing anode hydrogen partial pressure, exacerbating hydrogen supply non-uniformity, and altering the water balance. Notably, the latter two factors interact and collectively affect in-plane uniformity, leading to complex performance characteristics under hydrogen dilution conditions. Furthermore, the performance loss due to hydrogen dilution observed in this study is more pronounced than previously reported, primarily due to low catalyst loading and in-plane non-uniformity resulting from scale expansion. Nevertheless, at medium to low current densities and high HSR conditions, where the impact of hydrogen dilution is diminished, moderate hydrogen dilution can be permitted to enhance hydrogen utilization. Based on the data collected, this study maps the boundary for hydrogen dilution constrained by performance loss, offering valuable insights into the design and optimization of future control strategies.